The motile behavior of human skin fibroblasts from biopsies of differently aged adult donors was tested by the technique of phagokinetic tracks (Albrecht-Buehler, Cell ll, 359, 1977). In this technique, the migrating cells remove small gold particles along their way on a densely particle coated substrate thus recording their own locomotion by a particle-free track. The study continues to be carried out as a blind test, i.e., the donor age of the different tested cell lines will not be disclosed to us until the experiments are completed. Therefore, we cannot discuss as yet a relationship between donor age and motile behavior. Nevertheless, we can report dramatic differences in the motile behavior of the tested lines, although the cells do not seem to differ in their morphology. The differences concern the speed of locomotion, the frequency of cellular extensions to the sides of the track, and the persistence by which cells remain in a non-motile state after reaching confluency.